15,484 research outputs found
Entanglement Entropy of the Low-Lying Excited States and Critical Properties of an Exactly Solvable Two-Leg Spin Ladder with Three-Spin Interactions
In this work, we investigate an exactly solvable two-leg spin ladder with
three-spin interactions. We obtain analytically the finite-size corrections of
the low-lying energies and determine the central charge as well as the scaling
dimensions. The model considered in this work has the same universality class
of critical behavior of the XX chain with central charge c=1. By using the
correlation matrix method, we also study the finite-size corrections of the
Renyi entropy of the ground state and of the excited states. Our results are in
agreement with the predictions of the conformal field theory.Comment: 10 pages, 6 figures, 2 table
Composite Higgs to two Photons and Gluons
We introduce a simple framework to estimate the composite Higgs boson
coupling to two-photon in Technicolor extensions of the standard model. The
same framework allows us to predict the composite Higgs to two-gluon process.
We compare the decay rates with the standard model ones and show that the
corrections are typically of order one. We suggest, therefore, that the
two-photon decay process can be efficiently used to disentangle a light
composite Higgs from the standard model one. We also show that the Tevatron
results for the gluon-gluon fusion production of the Higgs either exclude the
techniquarks to carry color charges to the 95% confidence level, if the
composite Higgs is light, or that the latter must be heavier than around 200
GeV.Comment: RevTex 7 pages, 6 figure
Supergravity Computations without Gravity Complications
The conformal compensator formalism is a convenient and versatile
representation of supergravity (SUGRA) obtained by gauge fixing conformal
SUGRA. Unfortunately, practical calculations often require cumbersome
manipulations of component field terms involving the full gravity multiplet. In
this paper, we derive an alternative gauge fixing for conformal SUGRA which
decouples these gravity complications from SUGRA computations. This yields a
simplified tree-level action for the matter fields in SUGRA which can be
expressed compactly in terms of superfields and a modified conformal
compensator. Phenomenologically relevant quantities such as the scalar
potential and fermion mass matrix are then straightforwardly obtained by
expanding the action in superspace.Comment: 10 pages; v2: references update
Critical and Multicritical Semi-Random (1+d)-Dimensional Lattices and Hard Objects in d Dimensions
We investigate models of (1+d)-D Lorentzian semi-random lattices with one
random (space-like) direction and d regular (time-like) ones. We prove a
general inversion formula expressing the partition function of these models as
the inverse of that of hard objects in d dimensions. This allows for an exact
solution of a variety of new models including critical and multicritical
generalized (1+1)-D Lorentzian surfaces, with fractal dimensions ,
k=1,2,3,..., as well as a new model of (1+2)-D critical tetrahedral complexes,
with fractal dimension . Critical exponents and universal scaling
functions follow from this solution. We finally establish a general connection
between (1+d)-D Lorentzian lattices and directed-site lattice animals in (1+d)
dimensions.Comment: 44 pages, 15 figures, tex, harvmac, epsf, references adde
Anomaly Matching in Gauge Theories at Finite Matter Density
We investigate the application of 't Hooft's anomaly matching conditions to
gauge theories at finite matter density. We show that the matching conditions
constrain the low-energy quasiparticle spectrum associated with possible
realizations of global symmetries.Comment: 11 pages, 1 figure, LaTeX. Section C is corrected and added
reference
Multitasking associative networks
We introduce a bipartite, diluted and frustrated, network as a sparse
restricted Boltzman machine and we show its thermodynamical equivalence to an
associative working memory able to retrieve multiple patterns in parallel
without falling into spurious states typical of classical neural networks. We
focus on systems processing in parallel a finite (up to logarithmic growth in
the volume) amount of patterns, mirroring the low-level storage of standard
Amit-Gutfreund-Sompolinsky theory. Results obtained trough statistical
mechanics, signal-to-noise technique and Monte Carlo simulations are overall in
perfect agreement and carry interesting biological insights. Indeed, these
associative networks pave new perspectives in the understanding of multitasking
features expressed by complex systems, e.g. neural and immune networks.Comment: to appear on Phys.Rev.Let
Multicritical continuous random trees
We introduce generalizations of Aldous' Brownian Continuous Random Tree as
scaling limits for multicritical models of discrete trees. These discrete
models involve trees with fine-tuned vertex-dependent weights ensuring a k-th
root singularity in their generating function. The scaling limit involves
continuous trees with branching points of order up to k+1. We derive explicit
integral representations for the average profile of this k-th order
multicritical continuous random tree, as well as for its history distributions
measuring multi-point correlations. The latter distributions involve
non-positive universal weights at the branching points together with fractional
derivative couplings. We prove universality by rederiving the same results
within a purely continuous axiomatic approach based on the resolution of a set
of consistency relations for the multi-point correlations. The average profile
is shown to obey a fractional differential equation whose solution involves
hypergeometric functions and matches the integral formula of the discrete
approach.Comment: 34 pages, 12 figures, uses lanlmac, hyperbasics, eps
Local-channel-induced rise of quantum correlations in continuous-variable systems
It was recently discovered that the quantum correlations of a pair of
disentangled qubits, as measured by the quantum discord, can increase solely
because of their interaction with a local dissipative bath. Here, we show that
a similar phenomenon can occur in continuous-variable bipartite systems. To
this aim, we consider a class of two-mode squeezed thermal states and study the
behavior of Gaussian quantum discord under various local Markovian non-unitary
channels. While these in general cause a monotonic drop of quantum
correlations, an initial rise can take place with a thermal-noise channel.Comment: 6 pages, 4 figure
Folding of the Triangular Lattice in the FCC Lattice with Quenched Random Spontaneous Curvature
We study the folding of the regular two-dimensional triangular lattice
embedded in the regular three-dimensional Face Centered Cubic lattice, in the
presence of quenched random spontaneous curvature. We consider two types of
quenched randomness: (1) a ``physical'' randomness arising from a prior random
folding of the lattice, creating a prefered spontaneous curvature on the bonds;
(2) a simple randomness where the spontaneous curvature is chosen at random
independently on each bond. We study the folding transitions of the two models
within the hexagon approximation of the Cluster Variation Method. Depending on
the type of randomness, the system shows different behaviors. We finally
discuss a Hopfield-like model as an extension of the physical randomness
problem to account for the case where several different configurations are
stored in the prior pre-folding process.Comment: 12 pages, Tex (harvmac.tex), 4 figures. J.Phys.A (in press
Entropy of Folding of the Triangular Lattice
The problem of counting the different ways of folding the planar triangular
lattice is shown to be equivalent to that of counting the possible 3-colorings
of its bonds, a dual version of the 3-coloring problem of the hexagonal lattice
solved by Baxter. The folding entropy Log q per triangle is thus given by
Baxter's formula q=sqrt(3)(Gamma[1/3])^(3/2)/2pi =1.2087...Comment: 9 pages, harvmac, epsf, uuencoded, 5 figures included, Saclay
preprint T/9401
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